Seekbar disabling after video completion

May I ask: Why would you want to permit them to drag and manipulate the video seekbar on their first pass through the video? The intuitive behavior is to drag and manipulate the video after watching it through at least once. (And as it sounds like you know, that's how the controls are configured in SL.) If the intention is to require them to click a "replay" button before the seekbar is disabled, you may simply need to duplicate the slide and video; on the first pass, they can click and drag the seekbar as they want, but when they click a Replay button (you would create that), they actually advance to the next slide, which has the controls locked down, and then they could watch the video again.

But as I said, this seems almost counter-intuitive, and potentially very frustrating for your learners.

Thank you. In short, I have a need to create a module where the user can skim through the video if they wish. They don't have to watch all of the instructional content, as they may know some of the instructions within it. I want them to be able to do the same when they replay the video. I just don't want them to be able to use the seekbar after the video finishes, as the functionality just isn't there at that point, which is just confusing for the user. I want them to click on replay to repeat the functions from the first watch (which I have created and that all works fine).

Your best option is to use JavaScript, as this functionality isn't built-in by default. Run the following script when the timeline ends on a slide:

const seek = document.querySelector('#seek');
const reset = document.querySelector('#reset');

seek.style.pointerEvents = 'none';

reset.addEventListener('click', function () {
  seek.style.pointerEvents = 'all';
});